By the beginning of 2015, the Russian military successfully completed the initial testing phase of a new-generation robotic spacecraft designed to inspect and destroy enemy satellites in orbit, reliable sources said. A much more sophisticated vehicle than previous-generation anti-satellite systems, also known as ASAT, the new satellite killer proved its ability to make a very close approach to its targets and send close-up images of them to ground control. However the ultimate goal of the new vehicle would be the destruction of foreign payloads, first of all, US military satellites. Following the launch of two test satellites under the cover names Kosmos-2491 and Kosmos-2499, the latest spacecraft in the series, designated Kosmos-2504, entered orbit on March 31, 2015, and, after a series of maneuvers, hit its test target around April 16. The orbital maneuvers continued in July.

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New-generation system

According to one source, by the beginning of 2015, the Russian killer satellite, most likely Kosmos-2499, had already passed near by and downlinked images of an American military satellite! So far, there was no confirmation of such an encounter by the US government. Although orbital parameters of US satellites are not officially published, amateur data allows to rule out the possibility of practically all known non-Russian satellites flying in matching orbits with Kosmos-2504 or its siblings, says Jonathan McDowell, a scientist at Harvard-Smithsonian Center for Astrophysics and a veteran space historian. As a result, a formation flying or a rendezvous with a low relative speed between the Russian and any foreign satellite, like the one observed between Kosmos-2499 and its Briz-KM stage would not be possible. However, "a fast flyby at a high relative velocity is certainly possible, and I can't rule that out," McDowell wrote in an e-mail.

With enough maneuverability, the new Russian anti-satellite vehicles could use lasers or small-size kinetic weapons instead of explosives and shrapnel to disable their targets. The miniature spacecraft could then back up and attack another satellite. However, with the relatively small size of observed Russian satellites, their maneuvering capability is likely limited. At the same time, they could be only precursors to larger, more capable spacecraft.

Highly clandestine tests of the latest Russian anti-satellite system coincided with the worsening of relations between the West and East over the crisis in Ukraine. In addition, years of joint Russian and Chinese efforts in the United Nations to introduce a ban on deployment of weapons in space has also gone nowhere due to the US position that such a treaty would be unverifiable and meaningless. Ironically, China and the US both proved that point by destroying orbital targets by missiles based on Earth.

Launch of Kosmos-2504

A Rockot booster launched three Gonets-M satellites No. 21, 22 and 23 comprising Block No. 14 of the Gonets-D1M network, and a classified military payload.

According to official media, the Rockot/Briz-KM lifted off on March 31, 2015, at 16:47:56 Moscow Time from Site 133 in Plesetsk. The Russian Ministry of Defense confirmed the on-time launch and the presence of a fourth military payload onboard the launch vehicle, which would receive the official designation Kosmos-2504. It could also have the designation 14F153. The payload section separated from the second stage of the launch vehicle at 16:53 and the spacecraft were expected to reach their orbit at 18:45 Moscow Time.

Orbital maneuvers

Western radar detected five objects (likely four satellites and their Briz-KM stage) in a 1,172 by 1,506-kilometer orbit with an inclination 82.5 degrees toward the Equator. In the public catalog of the US Strategic Command, these objects received designations 2015-020A, 2015-020B, 2015-020C and 2015-020D.

Within hours after the launch, Dutch amateur radio enthusiast Cees Bassa detected radio transmissions associated with Object 2015-020D, which were identical to signals from previous maneuverable satellites -- Kosmos-2491 and Kosmos-2499.

Based on orbital parameters of Object D, it was clear that Kosmos-2504 had separated from the Briz-KM after the stage had maneuvered to its "burial" orbit, instead of being released along with the trio of Gonets satellites, as Kosmos-2491 and Kosmos-2499 had previously done, observers reported on the online forum of the Novosti Kosmonavtiki magazine.

Western radar data indicated that on April 9, 2015, Kosmos-2504 had made a small maneuver, transitioning from a 1,171 by 1,505-kilometer orbit to a 1,173 by 1,508-kilometer orbit. Another series of maneuvers apparently began around April 13, culminating with a rendezvous with the Briz-KM stage, which had delivered it into orbit. On the evening of April 15, the two objects were estimated to be within 4.4 kilometers from each other and on April 16, within just 1.4 kilometers.

Moreover, around April 16, a dormant Briz-KM stage showed signs of climbing up slightly, or much more likely, being pushed to a higher orbit either deliberately or as a result of physical impact during docking.

However by the end of April 17, the two objects were detected splitting up again, with Kosmos-2504 still in the original rendezvous orbit and Briz-M now circling the Earth in a distinctively higher orbit.

New maneuvers in July 2015

Between July 2 and July 3, 2015, Kosmos-2504 made a sudden maneuver descending 53 kilometers, observers reported on the online forum of the Novosti Kosmonavtiki magazine. The satellite went from a 1,181 by 1,528-kilometer to a 1,124 by 1,476-kilometer orbit. The orbital inclination changed slightly from 82.49 to 82.68 degrees.

By October 8, 2015, Kosmos-2504 manuevered toward the Briz-KM upper stage that delivered it into orbit and remained in its vicinity for the remainder of the month.

Kosmos-2504 comes to life in 2017

Nearly two years after it had last made headlines, the mysterious Russian military satellite, Kosmos-2504, suddenly resumed its maneuvers. Its first noticeable movements since 2015 were detected on March 27, 2017. Remarkably, on April 20, Kosmos-2504, passed as close as 1,183 meters from Object 1999-025DPP, which is a remnant of a Chinese weather satellite, Fengyun-1C, destroyed on Jan 11, 2007, in an apparent test of China's anti-satellite missile. This piece of space junk is circling the Earth in a 848 by 736-kilometer orbit with an inclination 98.87 degrees toward the Equator, according to NORAD. It is one of the hundreds of fragments left over from the explosion and trackable by radar.

The Russian spacecraft then conducted another maneuver between April 18 and April 19, 2017. By April 20, 2017, the satellite's perigee was reduced to 627 kilometers from 1,145 kilometers on March 30. During the same period, the apogee was lowered slightly from 1,507 to 1,502 kilometers.

Even more surprisingly, the satellite's predecessor, Kosmos-2499, also appeared making a maneuver around the same time!